1. Field of the Invention
The present invention relates to an improved disc brake and, more particularly, to an improvement of a multiple disc brake for use in a large-size vehicle such as a bus or truck which generates heat due to friction.
2. Description of the Related Art
There has been known a multiple disc brake apparatus for use in a large-size vehicles such as buses and trucks, in which apparatus at least two rotors and at least three pads are alternately arranged.
The construction and operation of the conventional multiple disc brake apparatus will be described with reference to FIGS. 1 and 2 which show also an embodiment of the present invention.
A shaft 1 rotates together with a vehicle wheel. A hub 2 is mounted on an outer periphery of the shaft 1 such that the hub 2 is unrotatable with respect to the shaft 1. Two annular rotors 3 are engaged with a serration engaging portion S.sub.1 provided between an outer peripheral surface of the hub 2 and an inner peripheral surface of each of the rotors 3, so that the rotors 3 are movable in a direction of a longitudinal axis of the shaft 1.
A housing 4 is secured to an unrotatable portion of the vehicle such as a suspension mechanism. Three annular pads 5a and 5b are engaged with a serration engaging part S.sub.2 provided between an inner peripheral surface of the housing 4 and an outer peripheral surface of each of the pads 5a and 5b, so that the pads 5a, 5b are movable in the direction of the longitudinal axis of the shaft 1. The inner and outer pads 5a comprise a rear plate 7 and a friction member 6 secured to the rear plate 7. The center pad 5b comprises merely of a friction member 6. The pads 5a, 5b and the rotors 3 are alternately arranged in such a manner that the three pads 5a, 5b sandwich the two rotors 3.
Four cylinder members 8 (only one is described in FIG. 1) are mounted on the housing 4 at an equal interval in a circumferential direction thereof. A piston 9 is urged against the pads 5a, 5b by supplying a pressurized brake fluid to the interior of the cylinder member 8 through a fluid supply pipe 10 fitted to the cylinder member 8.
The conventional disc brake apparatus is further provided with a cylinder member air discharging valve 11 and bearings 12 which allow the shaft 1 to rotate with respect to the housing 4.
In the multiple disc brake apparatus thus constructed, when the pressurized brake fluid is supplied to the cylinder member 8 through the fluid supply pipe 10, the piston 9 is forced from the cylinder member 8 so that the rotors 3 and the friction members 6 of the pads 5a, 5b are strongly urged against each other to produce a frictional force which is supplied to the shaft 1 as a braking force. During the braking operation, a brake torque is transmitted to the housing 4 through the serration engaging member S.sub.2.
The conventional multiple disc brake apparatus thus constructed suffers from the following problems.
During the braking operation, heat is generated by a frictional engagement between the rotors 3 and the pads 5a, 5b. When the braking operation is actuated while the vehicle is travelling at a high speed, or when the braking operation is frequently actuated while the vehicle travels down a mountain road, the heat generated during the braking operation will be excessively large. Therefore, the conventional brake apparatus suffers from a vapor lock phenomenon caused by a vaporization of the brake fluid when the heat is transmitted to the brake fluid in the cylinder member 8.
Unexamined Japanese Patent Application (OPI) No. 61-149624 discloses a brake apparatus in which a housing is separately provided from a cylinder member. However, it does not teach or suggest that the heat generated during the braking operation is to be prevented from being transmitted to the cylinder member.
Further, Japanese Patent No. 46-17846 discloses a brake apparatus in which a heat-resistant member is provided between a housing and a pad and between a piston and the pad. However, in this Japanese patent, a large torque produced during the braking operation is applied to the heat-resistant member. Therefore, the brake apparatus of this Japanese patent would be poor in durability and reliability.